Crystal Chemistry and Structure of Vesuvianite

The chemical variations of vesuvianite samples from 16 different localities, eleven in Japan, two in Norway, one in Canada, Pakistan, and Russia, have been examined using electron-microprobe analyses. For some of selected samples boron content was also examined. Results of analyses were reduced to formula unit on the basis of 50 cations excluding boron. The crystal structures of six high-symmetry (P4/nnc) vesuvianite from Japan and three low-symmetry (non-P4/nnc) vesuvianitei from Japan, Pakistan and Norway were determined by single-crystal X-ray diffraction method. The nine crystals have the following cell parameters; a = 15.568(2), 15.559(3), 15.528(3), 15.472(2), 15.564(2), 15.559(3), 15.572(2), 15.759(1), 15.563(2); c = 11.790(1), 11.797(2), 11.755(2), 11.754(1), 11.841(1), 11.826(2), 11.833(2), 11.727(1), 11.818(1) Å, respectively. The structure refinements were carried out in the space group P4/nnc, P4/n and P4nc. The final R indices for 1821, 1493, 1357, 1415, 3024, 3743, 2053, 1745 and 1873 independent reflections are 0.038, 0.031, 0.040, 0.032, 0.063, 0.082, 0.038, 0.039 and 0.060, respectively. The EXAFS method was also used to investigate the local environment of the Cu and Mn ions in the crystal structure of vesuvianites from Norway and Japan. The chemical analyses of low-symmetry vesuvianites indicate a very small amount of F and almost negligible Cl while high-symmetry one contains a considerable amount of F and Cl. The high-symmetry vesuvianite can contain Cl- ions preferentially occupying the O(10) site which is split into two sites; one is occupied by Cl- and the other by F-. The chemical compositions of high-symmetry vesuvianites are more variable than those of low-symmetry vesuvianites. The ordering of cation and vacancy in the two alternately and statistically occupied sites in a unit cell causes the lowering of the symmetry from the space group P4/nnc to P4/n or P4nc. The ordering scheme of P4nc structure is firstly confirmed in this paper. In the three low-symmetry vesuvianites, the refined site occupancy ratios for occupied (B(a) and C(a)) and vacant sites (B(b) and C(b)) are 63:37, 62:38 and 92:8 (%), respectively, and the values suggest that the ordering in these crystals is not complete. In low-symmetry vesuvianite, the satisfaction of the local charge balance on O(10) anions requires alternate occupancy of oxygen and hydroxyl with an associated hydrogen bond and ordering sequences of cations. In Cl- and F-bearing high-symmetry vesuvianite, on the other hand, occupying of Cl and F in O(10) sites interrupts the sequences of cations and vacancies along the fourfold rotation axes. Boron-bearing vesuvianite from Russia contain more Mg and less Al than those of boron-free vesuvianite. Boron occupies the additional cation sites, tetrahedrally coordinated site at the 8h position and triangularly coordinated site at the 2a position. The excess of the scattering power at these sites derived from the measured amounts of boron indicates that some elements other than boron should occupy in boron positions

Liesegang Texture Found in Pyrophyllite Ore Deposits, Shobara district, Southwest Japan: Photograph collection

Liesegang textures are commonly occurred in pyrophyllite ore deposits in Shobara district, Southewest Japan. Color photographs of mode of occurrence, handspecimens and characteristic microtextures are presented. At the Sankin-motoyama outcrop, Liesegang texture is developed more than 500m long along the strike direction of the host rhyolitic rocks. The Liesegang texture is developed in the pyrophyllite rich zone and the texture is characterized by alternate of light and deep color bands. The light color is white to grey and the deep color is rather various such as brown, purple and grey. Two types of bands are recognizable, one is parallel and the other is perpendicular to the bedding plane of host rhyollitic rocks, respectively. The former is found in the marginal part whereas the latter mainly in the central part. Cylindrical Liesegang ring whose size is in the range from 10 to 50 cm is also common. The shape of the central core is various such as sphere, ellipsoid and cube. The band width of the Liesegang texture is various from few millimeters to several tens centimeters. Under the microscope, double or triple hematite rings are commonly observed in the deep color part and towards the light color part, shape of the rings becomes more and more irregular. The boundary of light and deep color bands is clearly recognized under the microscope by sudden development of opaque minerals in the deep color part and the boundary is irregular compared with straight appearance observed in the out crop. Detailed description of the texture will be appeared elsewhere

Micro-textures of Hematite in the Liesegang Rocks, Found in Pyrophyllite Deposits, Shobara District, Southwest Japan.

Characteristic micro-textures of hematite found commonly in the Liesegang rocks collected from pyrophyllite ore deposits, Shobara district, southwest Japan were investigated. Detailed observations of the Liesegang rocks under the high magnification reflection microscope with oil immersion lens reveal that almost all of opaque grains are composed of needle-shaped very fine crystals with less than few microns in width and 5-10 microns in length. Moreover, doughnut-like texture, which is characteristic in the Liesegang rock (Yamashita et al., 1996), is mainly composed of the needle-shaped fine crystals. In many cases, the rings are composed of radiated aggregates of the needle-shaped hematite crystals. The size of the most predominant rings is less than 10µm in diameter, and double, triple and multi rings are also common. The optical properties of these opaque crystals under the reflection microscope are almost similar to those of ordinary hematite, i.e., weak but noticeable bireflectance and distinct anisotropism (e.g., Uytenbogaardt, 1971). X-ray powder diffraction data indicate that most of the opaque minerals are hematite with small amount of goethite. However, under the reflection microscope, distinguishment of the two minerals is not possible

Spherulitic Textures Found in Pyrophyllite Ore Deposits, Shobara District, Southwest Japan: Photograph Collection

Spherulitic textures are commonly found in pyrophyllite ore deposits in Shobara district, Hiroshima Prefecture, Japan. Color photographs of the mode of occurrence, hand specimens and characteristic micro-textures are presented. The spherulitic textures occur mainly in the upper most horizon of the ore deposits, i.e., in pyrophyllite zone and weakly altered host rhyolitic rocks. The size of the spherulites is from few millimeters to several centimeters in diameter and the spherulites with several millimeters diameter is the most predominant. Color of the spherulites is also variable such as grey, dark blue, dark purple and greenish color. Under the microscope, the textures can be divided into two types, one is "radiation" and the other is "aggregation" types, respectively. The aggregation type is further subdivided into a) with fine grain rim and b) with coarse grain rim. The constituent minerals of the spherulite are feldspar, quartz, pyrophyllite, sericite, diaspore, hematite and goethite

ベスビアナイトの結晶化学と結晶構造

The chemical variation of vesuvianite samples from 16 different localities, eleven in Japan, two in Norway, one in Canada, Pakistan, and Russia, have been examined using electron-microprobe analyses. For some of selected samples boron content was also examined. Results of analyses were reduced to formula unit on the basis of 50 cations excluding B. The crystal structures of six high-symmetry (P4/nnc) vesuvianite from Japan and three low-symmetry (non-P4/nnc) vesuvianites from Japan, Pakistan and Norway were determined by single-crystal X-ray diffraction method. The nine crystals have the following cell parameters; a = 15.568(2), 15.559(3), 15.528(3), 15.472(2), 15.564(2), 15.559(3), 15.572(2), 15.759(1), 15.563(2); c = 11.790(1), 11.797(2), 11.755(2), 11.754(1), 11.841(1), 11.826(2), 11.833(2), 11.727(1), 11.818(1) Å, respectively. The structure refinements were carried out in the space group P4/nne, P4/n and P4nc. The final R indices for 1821, 1493, 1357, 1415, 3024, 3743, 2053, 1745 and 1873 independent reflections are 0.038, 0.031, 0.040, 0.032, 0.063, 0.082, 0.038, 0.039 and 0.042, respectively. The EXAFS method was also used to investigate the local environment of the Cu and Mn ions in the crystal structure of vesuvianites from Norway and Japan. The chemical analyses of low-symmetry vesuvianites indicate a very small amount of F and almost negligible Cl while high-symmetry one contains a considerable amount of F and Cl. The high-symmetry vesuvianite can contain Cl- ions preferentially occupying the O(10) site which is split into two sites; one is occupied by Cl- and the other by F. The chemical compositions of high-symmetry vesuvianites are more variable than those of low-symmetry vesuvianites. The ordering of cation and vacancy in the two alternately and statistically occupied sites in a unit cell causes the lowering of the symmetry from the space group P4/nnc to P4/n or P4nc. The ordering scheme of P4nc structure is firstly confirmed in this paper. In the three low-symmetry vesuvianites, the refined site occupancy ratios for occupied (B(a) and C(a)) and vacant sites (B(b) and C(b)) are 63:37, 62:38 and 92:8 (%), respectively, and the values suggest that the ordering in these crystals is not complete. In low-symmetry vesuvianite, the satisfaction of the local charge balance on O(10) anions requires alternate occupancy of oxygen and hydroxyl with an associated hydrogen bond and ordering sequences of cations. In Cl- and F-bearing high-symmetry vesuvianite, on the other hand, occupying of Cl and F in O(10) sites interrupts the sequences of cations and vacancies along the fourfold rotation axes. Boron-bearing vesuvianite from Russia contain more Mg and less Al than those of boron-free vesuvianite. Boron occupies the additional cation sites, tetrahedrally coordinated site at the 8h position and triangularly coordinated site at the 2a position. The excess of the scattering power at these sites derived from the measured amounts of boron indicates that some elements other than boron should occupy in boron positions.CONTENTS I.Introduction / p1 II.Experimental / p5 　A.Specimens used in this study / p5 　B.Electron-microprobe analysis / p5 　C.Structural analyses / p5 III.Result and discussion / p10 　A.Chemistry / p10 　B.Structure / p12 IV.Conclusion / p42 References / p44広島大学(Hiroshima University)博士(理学)Physical Sciencedoctora